Pennsylvania Sen. Arlen Specter’s party switch is one of those developments that both reflects the depth of the problems facing the GOP and could begin a new chapter for some Democratic officeholders who will face additional political challenges down the road.

[IMGCAP(1)]Republican strategists are downright gloomy over the gleeful reaction of conservative activists to Specter’s exit.

To those conservatives, Specter was never a reliable Republican anyway, and they see his moderate record — including his support for the stimulus package and the omnibus appropriations bill, for abortion rights and equal pay, and for a comprehensive solution on immigration reform — as diluting the party’s brand and empowering Senate Majority Leader Harry Reid (D-Nev.) and President Barack Obama.

But to Republican strategists, many of whom are personally conservative and have major policy differences with Specter, the grass roots’ reaction to the Senator’s party switch demonstrates that those activists don’t yet recognize the GOP’s fundamental problems and therefore aren’t ready to recruit candidates with broader appeal, particularly in parts of the country that are more liberal on cultural and environmental matters.

Thirty years ago, it was Democrats who imposed a rigid test on abortion, gun control and military spending, dismissing moderate Democrats as insufficiently pure. But party insiders learned their lesson after losing elections they assumed they would win, and the party started recruiting candidates who fit their districts.

The GOP is and will remain a conservative party. But unless its grass-roots activists come to accept the importance of nominating strong candidates who would be strong legislators, the party will be shut out of too many regions to enable it to be the strong national party that it was during the 1980s and 1990s.

Conservative activists don’t need to like Specter or agree with all of his votes, but cheering his exit from the party demonstrates that they don’t understand the seriousness of their political troubles or how they can rebuild their brand.

But if Specter’s switch is a headache for Senate Minority Leader Mitch McConnell (R-Ky.) and National Republican Senatorial Committee Chairman John Cornyn (Texas) — and it surely is — it is potentially an even bigger headache for Sen. Blanche Lincoln (D-Ark.) and dozens of other more moderate House and Senate Democrats who don’t agree with their party’s liberal wing and depend on the votes of moderate and conservative voters for their political survival.

Lincoln, who could well face a stiff challenge next year, surely would prefer that Republicans block some of the more liberal elements of the Obama/Congressional Democrats’ agenda, whether on health care, energy or government spending.

But now, with Specter switching teams and Democrats about to have 60 seats after Minnesota Democrat Al Franken is seated, Lincoln can’t count on the GOP restraining the Democratic majority. She and her more moderate allies in the Democratic Conference — from Nebraska’s Ben Nelson to Louisiana’s Mary Landrieu and even Indiana’s Evan Bayh — will have to be the ones who restrain their colleagues, if they have the political will.

This is also likely to be true for dozens of House Democrats who were elected from Southern and rural districts, and who will now be expected by their constituents to be more active in blocking higher taxes, bigger deficits and government expansion.

While those Democrats are still free to vote against their party — thereby establishing their “independence— and “moderation— — they also must know that their political standing back home rests as much on what their party does on Capitol Hill as how they vote as individual legislators.

For Lincoln, for example, voting against big-ticket, big-government Democratic initiatives may not be enough to inoculate her against Republican attacks blaming her party for the country’s direction.

Indeed, this is exactly what happened to Republicans across the country the past two cycles, in swing districts that were both Democratic-leaning and Republican-leaning. Many Republicans, such as then-Sens. Jim Talent (Mo.), Mike DeWine (Ohio) and Gordon Smith (Ore.) and then-Reps. Christopher Shays (Conn.), Rob Simmons (Conn.) and Nancy Johnson (Conn.), lost not because voters were particularly angry with them, but because voters were unhappy and angry with Washington and the GOP.

The good news for Republicans now is that Democrats own everything, giving greater salience to the GOP argument that voters (and contributors) need to support Republican candidates and the party’s campaign committees so that Democrats don’t have a “blank check.—

Specter’s switch may also embolden Democrats in the nation’s capital to move further left than what the country is comfortable with, causing a voter backlash and internal party fissures. This could, in turn, bring a new focus by the media on differences within the Democratic Party rather than on differences between the two parties.

Democrats have every reason to be euphoric about Specter’s switch, but at the end of the day, it may not be the game changer that they hope. For grass-roots Republicans, Specter’s switch ought not be an opportunity to celebrate, but rather, a time to consider the party’s stunning demise.